This invention relates to a coated coil spring having a coil spring wrapped in a coating member of soft synthetic resin foam to form a plurality of coated coil spring turns, wherein a helical clearance is formed between adjacent turns of said coated coil spring.
The coated coil spring offers the advantages of preventing noises arising from the collision between the coil turns, protecting said turns from damage, and suppressing the resonant vibration of the coated coil spring during application and consequently is accepted as, for example, the bedding of rolling stock.
The conventional coated coil spring is constructed by helically winding a wire completely wrapped in a substantially cylindrical rubber or synthetic resin foam with no helical clearance allowed between the respective turns. The coated coil spring proposed to date indeed has a very effective function, but is still found to leave much room for improvement. Namely, the conventional coated coil spring has the drawbacks that since not only the peripheral walls of the coil turns but also their interstices are wrapped in the coating material, the dynamic spring constant noticeably increases, thereby reducing the function of a coated coil spring in use; and therefore when the coated coil spring is used with a vehicle suspension device, the riding comfort is undesirably decreased.
To avoid the above-mentioned difficulties, the Japanese patent disclosure No. 57-120746 was published which set forth a coated coil spring whose turns were wrapped in a coating material with a slight helical clearance allowed between the respective coated turns.
However said patent disclosure No. 57-120746 has the drawbacks that when the helical clearance was unduly small and the coated coil spring was used in a vehicle suspension system, the dynamic spring constant became so large that riding comfort was reduced; and when the clearance was very large and the dynamic spring constant was decreased, surging of the coated coil spring and consequently a violent banging noise occurred.